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Does capitalization matter in email addresses?

Remember all those years you spent learning grammar rules in elementary and high school? “I before E except after C”, “don’t start a sentence with a conjunction” and so on.

Now, here we are, thoroughly entwined with the internet, and the rulebook is out the window. Sentences end with prepositions. Contractions are encouraged. Emojis are a free-for-all. 🙃🎉🥳

Which raises a question: What about capitalization?

In particular, does capitalization matter in emails? Does it make a difference if we capitalize the first letter of someone’s name or if we stick to lowercase? What happens if we accidentally add a capital letter when typing in a customer’s email address – will it still get delivered?

In this article, we’ll explore scenarios where capitals do matter and where they don’t. You’ll learn the best practices for using capitalization in emails to make sure your messages get read.


Table of contents


Do capitals matter in email addresses?

If you’re wondering, “do capital letters matter in email addresses?”, the simple answer here is no. Capitals don’t really matter in email addresses. They aren’t case-sensitive, unlike passwords.

That’s because modern mail servers essentially ignore capital letters. They see uppercase and lowercase letters as identical.

That means that all of these email accounts will go to the same place:

You may have noticed we said that the simple answer is no when asking does capitalization matter in email addresses. That’s because it is technically possible (though not common) for an uppercase and a lowercase email address to direct to two different mailboxes.

Here’s how it works. Each email address is a combination of two different parts:

  1. The domain name. Everything after the @ symbol (e.g. testemail.com)

  2. The unique address. Everything before the @ symbol (e.g. user93)

The domain part of the email address is entirely case insensitive, meaning capitals don’t make a difference, ever. If you type GMAIL.COM instead of gmail.com into your browser, your email will end up in the same place.

File Transfer Protocols (FTP) ignores capitalization in domain names and will send your email to the correct mailbox regardless.

With your unique address (the first part of your email, also known as the local part), things get a little more complicated.

For emails to be sent and received effectively between the various email providers (Gmail, Yahoo, Outlook, etc.), every email company needs to adhere to the same email protocol.

Over the last 50 or so years, this set of rules (known as Request for Comments, or RFC) has been revised and updated many times.

The latest version of RFC 5336, an SMTP (Simple Mail Transfer Protocol) extension, states that the first part of an email address (the unique address) can be case-sensitive.

Therefore, theoretically, there may be some servers containing two separate mailboxes for different capitalizations. For example, [email protected] and [email protected] would direct to different inboxes.

In practice, though, this rarely happens. It’s really only outdated email servers that use this approach. Virtually every major provider ignores capitalization.

In light of this information, the best practice is to stick to lowercase characters when choosing a new email address to avoid any potential problems.

There’s more to email addresses than just case sensitivity, however.

Can you use international symbols in an email address?

In short, yes.

​​RFC 6530 allows for the following types of international symbols:

  • Traditional Chinese characters: 喬治@屋企.香港

  • Latin alphabet with diacritics: jorgé@example.com

  • Japanese characters: ジョージ@黒川.日本

  • Greek alphabet: Γεώργιος@παράδειγμα.δοκιμή

  • Devanagari characters: जोर्गे@डाटामेल.भारत

  • Cyrillic characters: Джордж@с-балалайкой.рф

However, it is worth noting that not all email servers will be compliant with RFC 6530.

Outdated RFC 5322 servers won’t be able to handle such addresses. Luckily, you aren’t likely to come across many outdated servers because most people use major clients like Gmail and Outlook.

Still, if you’re going to create a mail address with international letters, it may be worth owning a second using only the Latin alphabet.

For instance, for jorgé@yourdomain.com, you might also create [email protected] and direct it to the same mailbox, so you can still receive emails if senders forget the diacritic.

Can you use numbers in an email address?

Yes, numbers are fair game in email addresses.

However, numbers are uncommon in the professional context. Some larger companies use numbers to delineate between different staff members with the same name (for example, there might be multiple Sarahs at an organization), though best practice would generally be to follow one of these naming conventions:

To maintain a professional appearance, you may wish to avoid using numerals in place of letters, such as [email protected]

Can you use special characters in an email address?

Only certain special characters can be used in email addresses.

Periods ( . ) and underscores ( _ ) are most common, but the following special characters can also be used:

! # $ % & ' * + - / = ? ^ _ ` { | } ~

There are a few other rules around using special characters in an email address:

  • Periods (or full stops) can’t be used as the first or last letter in an email address (such as [email protected] or [email protected])

  • The exception to the above is if quotation marks are used (“.yourname”@company.com is acceptable)

  • You can’t have two periods in a row (e.g. [email protected])

  • The max length is 64 characters

" ( ) , : ; < > @ [ \ ] are all also allowed, but with restrictions, and since many email servers don’t read them (Gmail addresses, for instance) best practice is to not use these special characters as they can make an email address harder to remember.

How do email services handle different cases?

The five major services (Gmail, Yahoo Mail, Hotmail, Outlook, Apple Mail) all treat addresses as case-insensitive.

There is no official list of email services that treat email addresses as case-sensitive and any that still do are outdated and likely to be rarely used.

What characters should I avoid in my email address?

The primary characters that can be used for email addresses are:

  • Latin letters A–Z

  • Numerals 0–9

  • The following special characters: . ! # $ % & ' * + - / = ? ^ _ ` { | } ~

Best practice would be to avoid any other characters when choosing an email address. This will help ensure you can send and receive emails correctly and avoid ending up in a spam box.


Best practices for using capitalization in email

We’ve cleared up the question around using capitals in email addresses, but what about in headlines and body copy?

In this next section, we’re going to switch gears a little and focus on email etiquette and the best practices for using capitalization in your sales and marketing emails.

Avoid using capitalization in subject lines

The accepted best practice is to avoid overusing capitalization in subject lines. By this, we’re talking about full caps, as in “THIS IS MY EMAIL SUBJECT LINE”.

While some marketers have A/B tested all-caps subject lines and received good results (higher open rates), the problem with this approach is that you risk triggering a spam filter.

Fully-capitalized email subject lines can appear spammy as capitalization is often used as a tool for conveying urgency (a tactic scammers rely on). Therefore, even if your email is legitimate, your customer’s spam filter might decide not to let you through.

Test completely lowercase subject lines

On the other hand, writing email subject lines entirely in lowercase (small letters) can be beneficial.

Some marketers find that lowercase subject lines can increase email open rates. Others find the opposite.

While, like uppercase subject lines, the jury is still out (i.e. your results may vary), lowercase typically isn’t seen as a spam trigger, so it mitigates the risk of ending up in a spam folder.

However, the potential increase in click-through and reply rates aren’t the only factor to weigh up here.

Some audiences may view the use of lowercase as unprofessional (it is, after all, technically incorrect not to start a sentence with a capital letter). Others may prefer it.

Be careful not to assume that certain demographics, like younger generations who were brought up using the internet and “text-speak”, tend to be less concerned with traditional grammar rules.

The best advice here is to run your own tests.

If lowercase fits within your style guidelines (say, for example, your brand persona is on the casual end of the spectrum), set up an A/B test in your email marketing platform to determine whether or not fully-lowercase email subject lines make a difference with your audience.


Use capitalization in emails sparingly

So, do capital letters matter in email addresses? When it comes to the actual body copy in your emails, it’s generally best to use capitalization sparingly.

Most readers would interpret excessive capitalization as shouting, and nobody wants to be shouted at, even by their favorite brand.

This doesn’t mean, however, that you need to avoid capitalization entirely. Uppercase can be used as a way to convey emotion and excitement and to communicate a sense of urgency.

For example, if you’re an ecommerce brand using email marketing to promote an end-of-year sale, a small amount of capitalization in your email content might be appropriate, such as in this email from Designmodo.


Again, your use of capitalization in the email body copy will depend entirely on your brand style guidelines.

Use sentence case to appear more approachable

The majority of brands will avoid writing either fully-uppercase or fully-lowercase email subject lines, which leaves you with two options:

  1. Sentence case, as in This is my email subject line

  2. Title case, as in This Is My Email Subject Line

Title case is typically interpreted as slightly more formal and reads more like a news headline. Sentence case reads more casually.

Your choice to use either title case or sentence case should be based on your brand guidelines. If your goal is to position your brand as serious, formal and professional, title case might be a better solution all around.

If, on the other hand, your goal is to appear more approachable, fun and casual, sentence case might be a better fit.

Because sentence case is typically seen as more approachable, best practice is to use this style in sales-related emails. You might choose, for example, to use title case for marketing email communications and investor updates and sentence case for SDR email outreach.

Numerals in headlines can increase open rates

It’s well-understood that numerals (0–9) are incredibly powerful tools that, when used in blog headlines, can increase click-through rates several times over.

According to NN Group’s widely-cited eye-tracking study, consumers find numerals super compelling, particularly if those numbers are relevant to their current position.

For example, someone struggling with increasing email open rates is very likely to click through on an article titled “How we increased open rates by 73%”, compared to “How to increase email open rates.”

This same logic applies to email subject lines. Where possible, use numerals (rather than spelling out numbers) to improve your own open rates. Some useful examples include:

  • 7 things we learned from our latest product roll-out

  • We interviewed 3 top sales leaders about account-based selling

  • Can I book 5 minutes of your time?

  • What would it mean to reduce your admin costs by 23%?

Use emojis to resonate with younger audiences

The use of emojis (🙂😂🎉) in emails can be controversial.

Some, typically older generations, find it unprofessional. Others believe emojis can help portray meaning and make written text easier to interpret.

You’ll likely need to do some testing here and determine whether emojis fit within your brand guidelines.

As a general rule, if you’re selling to Gen Z and Millennials (who are the most likely to say emojis help convey meaning and emotion), then using emojis in your email marketing can help you resonate and relate to your audience.


Final thoughts

Do uppercase letters matter in email?

In the case of email address, no, but if we’re talking headlines or email body content, capitalization (or lack thereof) can be an incredibly helpful and subtle tool for influencing open and reply rates.

Remember, it’s all about what works for your audience, so test, analyze, optimize and repeat.

Pipedrive has a suite of tools to help you track and analyze email performance. Why not check them out for yourself with a 14-day free trial?

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